Numerous systems already been proposed for charging rechargeable batteries. For example, the following patent publications all relate to this field: FR-A-1 240 286; FR-A-1 533 378; U.S. Pat. No. 3,980,940; and U.S. Pat. No. 4,084,123.
French Pat. No. 1,240,286 describes an installation for charging rechargeable batteries and comprising a voltage generator feeding a plurality of charging stations. The charging stations are associated with respective resistances which are connected in series across the terminals of the voltage generator when the charging stations are empty. When a battery is connected to a charging station, the associated resistance is disconnected from the circuit. The battery is thus connected to the terminals of a voltage generator in series with the resistances or batteries of the other stations. In order to ensure that such an installation operates properly, the charging current which passes through the batteries must neither be too low, in which case the batteries charge too slowly, nor too high, in which case the batteries are soon damaged.
The value of the current flowing through the batteries connected to the charging stations is defined by the ratio of the supply voltage divided by the sum of the impedances of the resistances and batteries connected in series between the terminals of the voltage generator. Proper operation of this installation thus relies on the impedance of the batteries being constant and equal to the associated resistances which are disconnected when batteries are installed for charging. In practice, battery impedances vary from one battery to another, and they change with time. The installation described in document FR-A-1 240 286 is thus not entirely satisfactory.
French Pat. No. 1,533,378 describes another system for charging a rechargeable battery and comprising an AC voltage generator, and a half-wave rectifying diode connected in series with a resistance for limiting the charging current.
U.S. Pat. No. 3,980,940 relates to a system for equalizing the charge on a plurality of rechargeable batteries connected in series. The system comprises a set of impedances for respective connection to the terminals of different ones of the batteries. When charging, these impedances may be constituted by diodes having identical threshold voltages which define the maximum charge of each battery. When discharging, these impedances may be constituted simply by resistances which cause the batteries to discharge identically.
U.S. Pat. No. 4,084,123 proposes integrating a rectifier bridge in each battery pack so as to enable battery packs to be charged by connection to an AC voltage source.
Proposals have also been made for various kinds of electrical appliances which are portable and cordless. These appliances are powered by internal rechargeable batteries, and they are intended to be periodically placed on associated supports which include charging systems for keeping the batteries properly charged at all times, so that the appliances are constantly ready for use.
A portable electrical vacuum cleaner of this type is described, for example, in Black and Decker's British patent application published under the No. 2 432 857.
The present proliferation of cordless appliances of this type leads to the user buying and installing a large number of appliance supports, each including its own charging system.
Preferred embodiments of the present invention provide a simple, reliable and cheap system suitable for charging a plurality of rechargeable battery sets incorporated in respective cordless appliances, thereby avoiding the proliferation of charging systems.
An aim of the present invention is to provide a charging system suitable for charging a variable number of battery sets.
Another aim of the present invention is to provide a cheap modular system serving both as a charger for a plurality of battery sets and as a storage support for the bodies of portable electrical appliances and their accessories, with the system being readily adaptable by the user as a function of the appliances to be charged and stored.
Another aim of the present invention is to provide a system in which it is cheap and easy to extend a pre-existing installation to include a support for storing a newly-purchased appliance and for charging a battery set contained therein.
Another aim of the present invention is to provide a system for charging a plurality of battery sets without requiring any monitoring on the part of the user, and which can be used by a non-specialist.